Recently, the use of cellular automaton has become more prevalent. A cellular automaton is a fundamental construct in computer science. It is a system that applies simple rules to a string of cells to produce a new string of cells. Typically, the cells are binary and represented by black or white. The context of this system is a discrete space consisting of locations for each cell. This cellular space therefore consists of identical finite-state machines, each of which obeys the same set of rules locally. The neighbors with which an object interacts is defined for each system. The interactions are typically local and, thus, do not involve interactions with objects outside of the defined neighborhood. Hence, there are two parts to a cellular automata: a cellular space containing a string of individual cells that have a defined state associated with them and a transition rule(s) for updating the state of the cell. In principle, all objects are updated simultaneously.
The cellular automata is run starting from a seed and each update is referred to herein as a step. A cellular automata running certain rules has some computational properties that will be explained below. First, (for certain rules) the cellular automata is random in that the output from each step passes all reasonable statistical measures of randomness, regardless of the seed (except for all black or all white). Second, (again for certain rules) the cellular automata is ergotic in that all possible states are eventually reached before cycling. Third, the cellular automata is linear in time meaning that given a seed, the only way to compute the Tth state is to compute all intermediate states, regardless of whether a parallel computer (single processor per cell) is being used.
The use of a particular cellular automaton, known as Rule 30, to generate pseudo-random numbers was disclosed in S. Wolfram, Proceedings of Crypto '85, pp 429-432. The encryption key is only the initial state of the cellular automaton.
Data is encrypted often for security during transmission or storage. Several encryption techniques are well-known in the art. The use of an invertible dynamical system for encryption was also disclosed. P. Guan, “Cellular Automata Public-Key Cryptosystems,” Complex Systems 1, 1987. During the encryption phase the dynamical system is run in the forward direction.
U.S. Pat. No. 5,677,956, entitled “Method and Apparatus for Data Encryption/Decryption using Cellular Automata Transform,” discloses encrypting and decrypting data using a transform that is a function of input data and a basis. After the input data is received, a cellular automata basis is generated from key values specifying characteristics of a cellular automata space of at least one cell and at least one rule of interaction for the at least one cell. Using the generated cellular automata basis, the input data is transformed into encrypted or decrypted data. The transform involves a huge library of cryptographic keys derived from a family of cellular automata.
U.S. Pat. No. 6,381,695 discloses an encryption system that inhibits the decryption of encrypted data unless a decryption condition is satisfied, where decryption enabled time is designated as a decryption condition. Thus, this patent discloses a encryption system with time-dependent decryption.
None of these techniques disclose giving delayed decryption power to an independent recipient, without requiring an external clock or programmed key release by the creator.